The present invention relates to a compact laser processing fixture and, more particularly, to a fixture for holding one or more laser bars such that the front and rear facets of the individual laser devices on the bars remain exposed for further processing, such as facet coating or focused ion beam milling.
During the manufacture of laser devices there are certain processing steps that are to be performed on the front and rear facets of the individual devices. For ease of manufacture and process uniformity, these steps are best performed when the laser is in xe2x80x9cbarxe2x80x9d form, that is, subsequent to the step of cleaving a wafer into separate, rectangular-shaped xe2x80x9cbarsxe2x80x9d. Each bar may include, for example, a dozen or more individual laser devices formed along its length.
One set of processes that is best performed at this stage of fabrication is facet coating. The laser xe2x80x9cfacetsxe2x80x9d may be defined as the front and rear surfaces of the individual laser devices that are exposed by the wafer cleaving process. To form active devices, these facets are coated with, for example, a dielectric material with proper reflectivity properties. For optimum performance of an individual device, as well as all devices within a particular process batch run, these coatings should be as uniform as possible (both at the device level, as well as from device to device within a particular process run). Further, the laser bars need to be xe2x80x9cheldxe2x80x9d during the coating process such that the material being deposited as the coating may or may not overflow (as desired) onto the top or bottom surfaces. Other process steps, besides facet coating, are also best performed when the laser is in xe2x80x9cbarxe2x80x9d form. For example, any process that includes physical modification of the facet itself, such as by focused ion beam milling (see, for example, U.S. Pat. No. 5,625,617, xe2x80x9cNear-Field Optical Apparatus with Laser having a non-uniform emission face), is best performed before a laser bar is cleaved into individual devices. During an exemplary focused ion beam process, the features being introduced onto the facet surface may be as small as 5-10 nm. Therefore, the laser bar must be held at a precisely specified uniform height, as well as held in a manner that minimizes the potential for vibration of the bar(s). Additionally, since an exemplary laser bar is itself relatively small and fragile (on the order of 1 cm in length, 0.75 mm tall and about 0.1 mm thick), any fixturing used to hold the laser bar during processing must be able to hold the bar firmly and reliably, but without damage. Lastly, to provide for the most efficient processing, the laser fixturing apparatus should, in most situations, be able to hold multiple bars simultaneously within a single processing fixture.
These and other requirements of laser fabrication are addressed by the present invention, which relates to a compact laser processing fixture and, more particularly, to a fixture for precisely and rigidly holding one or more laser bars such that the front and rear facets of the individual laser devices on the bars remain exposed for further processing.
In accordance with the present invention, a laser processing fixture is formed to comprise a first, stationary jaw and a second, movable jaw. A pair of bar-support members are disposed underneath and extend between the jaws in a spaced-apart relationship. In accordance with the present invention, the movable jaw is normally pressed towards the stationary jaw by a spring member, but is also retractable by an external means to allow for one or more laser bars to be positioned between the jaws such that a facet of the bar rests upon the bar support members. In a preferred embodiment of the present invention, the bar support members are spaced a sufficient distance apart such that the portions of the bar that contact the bar support members are beyond the locations of the active laser devices within the laser bar. Once the bars are loaded, the external retraction mechanism is released and the movable jaw is pressed forward by the spring member to contact the exposed top (or bottom) surface of the laser bar. It is an advantage of the design of the present invention that the fixture will hold the bar facets at a precisely-controlled distance with respect to a pre-defined reference plane. This control is particularly required for operations such as focused ion beam milling, where the facet plane must lie within the narrow focal plane window of the focused ion beam.
It is a feature of the arrangement of the present invention that both the front and rear facets of the laser bar are simultaneously exposed, thereby limiting the amount of unloading and re-loading that needs to be performed during laser bar processing. Additionally, it is an aspect of the present invention that the bar support members are capable of being controlled by a positioning arrangement such that precise alignment of the laser bar with respect to the jaws/fixture may be achieved.
In one embodiment of the present invention, the bar support members may comprise a pair of tungsten wires. Alternatively, the bar support members may comprise a pair of vacuum-slotted support rails, where this alternative embodiment is useful in processing multiple laser bars. In an embodiment for processing multiple wafer bars, additional spacer elements of a predetermined geometry may be disposed between adjacent bars to allow for ease of separation of the laser bars subsequent to processing, as well as to either permit or prevent xe2x80x9cwrap aroundxe2x80x9d of the facet dielectric coating.
Other and further features and aspects of the present invention will become apparent during the course of the following discussion and by reference to the accompanying drawings.